1. Field of the Invention
The present invention relates to a fuel cell system and a control method therefor. More specifically, the present invention relates to a fuel cell system which charges a secondary battery that is detachably provided to the fuel cell system, and a control method therefor.
2. Description of the Related Art
In general, there is known a fuel cell system which supplies a load with electric power from at least one of the fuel cell and a secondary battery charged with power from the fuel cell. JP-A 2004-319367 discloses a technique in which power from a fuel cell is stored in a secondary battery, such as a lithium ion battery, while the power is also used to drive a load.
In the above fuel cell system, if the secondary battery is removed while the fuel cell is generating power, all the power, including the power necessary for driving the load and the power necessary for driving system components which are used to supply the fuel cell with fuel and oxygen, must be covered by the output from the fuel cell.
While the amount of power necessary for driving the system components is substantially constant, the amount of power necessary for driving the load can fluctuate widely depending on how the load is used. Because of this, there is a risk that if the amount of power necessary for driving the load increases after the secondary battery has been removed, it will become impossible to supply enough power for driving the system components. In other words, there has been a risk that the power generation of the fuel cell, i.e., the operation of the fuel cell system, will become unable to be sustained if the secondary battery has been removed. JP-A 2004-319367 does not disclose nor indicate a process or mechanism for performing removal of the secondary battery from the system during power generation by the fuel cell.